R-1 is limited to five years. It cannot be extended beyond five years, and in order to be able to get a new visa for another five years, you will need to be outside the US for one year.
In response to the second part of your question, a foreign national does not even have to be in the United States to become a legal permanent resident. For example, if the foreign nationals are abroad, they obtain immigrant visas and become LPRs when they enter. Then, they receive their green cards in the mail.
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